1. Technical Field
This invention relates to a process for preparing phosphine oxides having the general formula (2) which comprises reacting iminophosphoranes having the general formula (1) with phosphorus oxytrichloride and to a process of purifying the above described phosphine oxides. The present inventors previously found that the above described phosphine oxides are very effective as polymerization catalysts for polymerizing alkylene oxide compounds, as catalysts for producing oxyalkylene derivatives from epoxy compounds, or as curing catalysts for curing the raw material resin for IC sealing, and already filed an application for a patent on each of the above described catalysts (Japanese Patent Application No. 10-106745, Japanese Patent Laid-Open Nos. 11-302371 or 11-322901, etc.).
2. Prior Art
Except for the present inventors' patent documents, the only publicly-known literature on phosphine oxides having the general formula (2) is the one disclosed by G. N. Koidan et al., in Journal of General Chemistry of the USSR, 55, p1453 (1985).
In this literature, the compound referred to as iminotris(dimethylamino)phosphorane in this patent application, which is iminophosphorane having the general formula (1) whose R is a methyl group, is termed hexamethyltriamidophosphazo hydride and the compound referred to as tris[tris(dimethylamino) phosphoranylidenamino]phosphine oxide in this patent application, which is phosphine oxide having the general formula (2) whose R is a methyl group, is termed tris[tris(N,N-dimethylamido)phosphazo]phosphate.
And the compound referred to as aminotris(dimethylamino)phosphonium chloride in this patent application, which is aminophosphonium chloride having the general formula (3) whose R is a methyl group, is the same as the compound termed hexamethyltriamidophosphazo hydride hydrochloride and shown by the form of [HN.dbd.P(NMe.sub.2).sub.3 ].HCl in the above described literature. Hereinafter, for the above described three kinds of compounds the expressions of this application shall be used.
In the above literature, described is the reaction of tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide with methyl iodide. And a process for preparing tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide, the raw material of the above reaction, is disclosed.
The literature states that tris[tris(dimethylamino)phosphoranilidenamino]phosphine oxide was obtained in an isolation yield of 85% by, first, adding a solution of phosphorus oxytrichloride in petroleum ether to a solution of iminotris(dimethylamino) phosphorane in petroleum ether drop by drop at 20.degree. C. for 30 minutes while stirring the solution mixture so that the mole ratio of the above described phosphorane to phosphorus oxytrichloride becomes exactly 6:1, after that (the time is not specified), separating the precipitate of aminotris(dimethylamino)phosphonium chloride as a by-product, washing the above described precipitate with petroleum ether, concentrating the filtrate, followed by crystallizing the residue from a small amount of the petroleum ether.
However, when the present inventors carried out the preparation of tris[tris(dimethylamino)phosphoranilidenamino]phosphine oxide under the same conditions as above, even after the addition of phosphorus oxytrichloride at 20.degree. C. for 30 minutes, almost no object compound was produced, as shown in comparative example 5 below. After that, the reaction was proceeded at a raised temperature of 40.degree. C. for 24 hours, however, the reaction yield of an object compound was as low as about 60%. Even after the additional 48 hours of reaction, the reaction yield was about 73% at the most.
In addition, the above literature only states that tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide was obtained "by crystallizing the residue from a small amount of the petroleum ether", but does not describe in detail the recrystallization process. The present inventors attempted recrystallization of crude phosphine oxide in such a manner that, first precipitate was separated by filtration from the liquid reaction product obtained after the 48 hours' reaction at 40.degree. C., as described above, then the filtrate was concentrated to dry to become a solid.
As shown in comparative example 6 below, a small amount of crystal deposition was observed only after the filtrate was cooled to -10.degree. C., and the crystal could be finally gathered after the filtrate was cooled to an extremely low temperature of -20.degree. C. The isolation yield of the crystal, that is, the isolation yield of tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide was as low as 20%, and moreover, the crystal contained a large amount of chlorine ion (about 600 ppm). Such residue of chlorine ion is a very serious problem when the above described phosphine oxide is used as a curing catalyst for curing the raw material resin for IC sealing which is required to have an electrical insulating property.
In the case where tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide is prepared by reacting iminotris(dimethylamino) phosphorane with phosphorus oxytrichloride, if one molecule of iminotris(dimethylamino) phosphorane reacts with one molecule of phosphorus oxytrichloride, one molecule of hydrogen chloride is yield at the same time. This hydrogen chloride immediately reacts with iminotris(dimethylamino) phosphorane to yield ionic aminotris(dimethylamino)phosphonium chloride. Accordingly, 6 moles of iminotris(dimethylamino) phosphorane is required stoichiometrically so as to react all of the three chlorines of one mole of phosphorus oxytrichloride. This is expressed by the following reaction equation. EQU 6HN.dbd.P(NME.sub.2).sub.3 +O.dbd.PCl.sub.3.fwdarw.O.dbd.P [N.dbd.P(NMe.sub.2).sub.3 ].sub.3 +3[H.sub.2 N--P.sup.+ (NMe.sub.2).sub.3 ]Cl.sup.-
As shown in comparative example 7 below, in the purifying process described in the above described literature, when imino(dimethylamino) phosphorane was used in excess of that stoichiometrically required so as to increase yields, the unreacted residue of the above described phosphorane could not be removed sufficiently, which led to a decrease in purity of recrystallized tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide.
Thus, the above disclosed process for preparing tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide is still very insufficient as an industrial process in that: its reaction and isolation yields are low, the purification process for its product requires an extremely low temperature, the ionic compound yielded by its reaction cannot be removed sufficiently, and its unreacted raw material cannot be removed sufficiently when using one reactant in excess of that stoichiometrically required in order to increase yields.